ac fundamnetals manual

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--------------------------- --------------------------- INSTRUCTION MANUAL AC/DC FUNDAMANTAL TRAINER OPERATING MANUAL List of experiments Voltage measurement on the CRO RMS value measurement with the help of meters Frequency measurement on the CRO Step down transformer measurements

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Page 1: Ac Fundamnetals manual

------------------------------------------------------INSTRUCTION MANUAL

AC/DC FUNDAMANTAL TRAINEROPERATING MANUAL

List of experiments Voltage measurement on the CRO RMS value measurement with the help of meters Frequency measurement on the CRO Step down transformer measurements Diode rectification using half wave rectifier Diode rectification using full wave rectifier Diode rectification using bridge rectifier

Page 2: Ac Fundamnetals manual

EXPERIMENT NO1. MEASUREMENT OF THE VOLTAGE BETWEEN TWO POINTS ON THE WAVEFORM.

This technique can be used to measure peak to peak voltages.1. Apply the signal to be measured to the INPUT jack. Set the vertical MODE to the channel to be used. Set the vertical MODE to the channel to be used. Set the AC-GND-DC to AC, adjusting VOLTS/DIV and SWEEP TIME/DIV for a normal display. Set the VARIABLE control to CAL position.2. Using the CH POSITION control, adjust the waveform position such that one of the two points falls on a CRT graduation line and that the other is visible on the display screen.3. Using the horizontal POSITION control, adjust the second point to con incide with the centre vertical graduation line.4. Measure the vertical distance between the two points and multiply this by the setting of the VOLT/DIV control. When a 10:1 probe is used, further multiply the value by 10.When a 10:1 probe is used.Volts peak-to-peak = Vertical distance (div) X (VOLTS/DIV setting) X 10With direct measurementVoltage between 2 points = Vertical distance (div) x 2 points.

ExampleFor the example, the 2 points are seperated by 4.5 divisions vertically. Set the VOLTS/DIV setting be 0.2 V/div and the probe attenuation be 10:1.Substituting the given values:Voltage between two points = 4.5 (div) X 0.2 (V/div) X 10 = 9.0

EXPERIMENT NO2. FREQUENCY MEASUREMENTS

Frequency measurement are made by measuring the period of one cycle of waveform and taking the reciprocal of this time value as the frequency. Procedure1. Following the procedure described in section 5 "Time Measurement", measure the time of each cycle. The figure obtained in the signal period.2. Frequency is the the reciprocal of the period measured. Using the formula:

Page 3: Ac Fundamnetals manual

Frequency = 1/period.

ExampleA period of 40us is observed and measured.Assuming that SWEEP TIME/DIV indicated 5 us/div, sustituting the given value:Frequency = 1/(40us) = 25 kHz

EXPERIMENT NO 3.

STEP DOW N TRANSFORM ER

AC OUTPUT

VV

STEP DOW N TRANSFORM ERW ITH 2 -12V TAP P INGS

Measurement of the ac voltage at the output by varying the select knobs to find out the ac voltage.

To connect ac meter / cro probe to see the Vrms/Vpp voltages.

Page 4: Ac Fundamnetals manual

Measure the ac input voltage of primary voltage

Secondary voltage are tabulated on the tabular column.

The transformer

 

HALF WAVE RECTIFIERAim: -To study the characteristics of half wave and full wave rectifier. TheoryThe Half wave rectifier is a circuit, which converts an ac voltage to dc voltage. In the Half wave rectifier circuit shown above the transformer serves two purposes. It can be used to obtain the desired level of dc voltage (using step up or step down transformers). It provides isolation from the power line. The primary of the transformer is connected to ac supply. This induces an ac voltage across the secondary of the transformer. During the positive half cycle of the input voltage the polarity of the voltage across the secondary forward biases the diode. As a result a current IL flows through the load resistor, RL. The forward biased diode offers a very low resistance and hence the voltage drop across it is very small. Thus the voltage appearing across the load is practically the same as the input voltage at every instant. During the negative half cycle of the input voltage the polarity of the secondary voltage gets reversed. As a result, the diode is reverse biased. Practically no current flows through the circuit and almost no voltage is developed across the resistor. All input voltage appears across the diode itself. Hence we conclude that when the input voltage is going through its positive half cycle, output voltage is almost the same as the input voltage and during the negative half cycle no voltage is available across the load. This explains the unidirectional pulsating dc waveform obtained as output. The process of removing one half the input signals to establish a dc level is aptly called half wave rectification. Ripple FactorRipple factor is defined as the ratio of rms value of ac component to the dc component in the output. Ripple factor

Efficiency Efficiency,is the ratio of the dc output power to ac input power thus

Page 5: Ac Fundamnetals manual

Connection diagram half wave rectifier

Page 6: Ac Fundamnetals manual

AC FUNDAM ENTALS TRAINER

AM M ETERVOLTM ETER

STEP DOW N TRANSFORM ER

AC OUTPUT

mA

V

IN 400 7

IN 400 7

IN 400 7

RL

IN 400 7 L 200 mH

10 0 0µF25 V

10 0 µF25 V

+ +

S 1 S 2

VV

VV

LOAD RESISTOR10 0 E

15 0 E

220 E3 30 E 5 6 0 E

1K

470 E

RL

M AINS ON

STEP DOW N TRANSFORM ERW ITH 2-12V TAP PINGS

FILTER CI RCUIT

VOLTM ETER DC

VOLTM ETER AC M ETER

SELECTIONRECTIFIER CIRCUIT

Steps to perform on the kit Make the connection as per the connection diagram Ensure that , Connect should be all way right before switching on the trainer. Switch off the S1 and S2 (to Take the reading without capacitor filter. Switch on the power. Note down the reading in the voltmeter and ammeter. These reading are DC rectified values. See the ripple output on to the CRO to observe the waveform and ripple amplitude. Repeat the reading with capacitor and pi filter by switching on the Switch S1, S2. See the difference of

filtered output and without filtered output. Record the reading in the table. Find the practical values.

Page 7: Ac Fundamnetals manual

FULL WAVE RECTIFIER

2. FULL CENTER TAP RECTIFIER TheoryA Full wave center tap rectifier is a circuit, which converts an ac voltage into a pulsating dc voltage using both half cycles of the applied ac voltage. It uses two diodes of which one conducts during one half cycle while the other conducts during the other half cycle of the applied ac voltage.During the positive half cycle of the input voltage, diode D1 becomes forward biased and D2 becomes reverse biased. Hence D1 conducts and D2 remains OFF. The load current flows through D1 and the voltage drop across RL will be equal to the input voltage. Ripple FactorThe ripple factor for a Full Wave Rectifier is given by

The average voltage or the dc voltage available across the load resistance is

RMS value of the voltage at the load resistance is

Efficiency Efficiency, is the ratio of the dc output power to ac input power

Page 8: Ac Fundamnetals manual

The maximum efficiency of a Full Wave Rectifier is 81.2%.Rectifier with capacitive filterA capacitor filter connected directly across the load is shown above. The property of a capacitor is that it allows ac component and blocks dc component. The operation of the capacitor filter is to short the ripple to ground but leave the dc to appear at output when it is connected across the pulsating dc voltage.During the positive half cycle, the capacitor charges unto the peak vale of the transformer secondary voltage, Vm and will try to maintain this value as the full wave input drops to zero. Capacitor will discharge through RL slowly until the transformer secondary voltage again increases to a value greater than the capacitor voltage. The diode conducts for a period, which depends on the capacitor voltage. The diode will conduct when the transformer secondary voltage becomes more than the diode voltage. This is called the cut in voltage. The diode stops conducting when the transformer voltage becomes less than the diode voltage. This is called cut out voltage.Referring to the figure below, with slight approximation the ripple voltage can be assumed as triangular. From the cut-in point to the cut-out point, whatever charge the capacitor acquires is equal to the charge the capacitor has lost during the period of non-conduction, i.e., from cut-out point to the next cut-in point.The charge it has acquired

The charge it has lost

If the value of the capacitor is fairly large, or the value of the load resistance is very large, then it can be assumed that the time T2 is equal to half the periodic time of the waveform.

From the above assumptions, the ripple waveform will be triangular and its rms value is given by

Page 9: Ac Fundamnetals manual

The ripple may be decreased by increasing C or RL (both) with a resulting increase in the dc. Out put voltage.

ProcedureSteps to perform on the kit

Make the connection as per the connection diagram Ensure that , Connect should be all way right before switching on the trainer. Switch off the S1 and S2 (to Take the reading without capacitor filter. Switch on the power. Note down the reading in the voltmeter and ammeter. These reading are DC rectified values. See the ripple output on to the CRO to observe the waveform and ripple amplitude. Repeat the reading with capacitor and pi filter by switching on the Switch S1, S2. See the difference of

filtered output and without filtered output. Record the reading in the table. Find the practical values.

Bridge rectifier FULL WAVE BIRIDGE RECTIFIERTheoryThe Bridge rectifier is a circuit, which converts an ac voltage to dc voltage using both half cycles of the input ac voltage. The Bridge rectifier circuit is shown in the figure. The circuit has four diodes connected to form a bridge. The ac input voltage is applied to the diagonally opposite ends of the bridge. The load resistance is connected between the other two ends of the bridge.For the positive half cycle of the input ac voltage, diodes D1 and D3 conduct, whereas diodes D2 and D4 remain in the OFF state. The conducting diodes will be in series with the load resistance RL and hence the load current flows through RL. For the negative half cycle of the input ac voltage, diodes D2 and D4 conduct whereas, D1 and D3 remain OFF. The conducting diodes D2 and D4 will be in series with the load resistance RL and hence the current flows through RL in the same direction as in the previous half cycle. Thus a bi-directional wave is converted into a unidirectional wave.

Page 10: Ac Fundamnetals manual

Waveforms

Page 11: Ac Fundamnetals manual

Connection diagram Full Wave bridge Rectifier

Page 12: Ac Fundamnetals manual

AC FUNDAM ENTALS TRAINER

AM M ETERVOLTM ETER

STEP DOW N TRANSFORM ER

AC OUTPUT

mA

V

IN 400 7

IN 400 7

IN 400 7

RL

IN 400 7 L 200 mH

10 0 0µF25 V

10 0 µF25 V

+ +

S 1 S 2

VV

VV

LOAD RESISTOR10 0 E

15 0 E

220 E3 30 E 5 6 0 E

1K

470 E

RL

M AINS ON

STEP DOW N TRANSFORM ERW ITH 2-12V TAP PINGS

FILTER CI RCUIT

VOLTM ETER DC

VOLTM ETER AC M ETER

SELECTIONRECTIFIER CIRCUIT

Connection diagram bridge rectifierSteps to perform on the kit

Make the connection as per the connection diagram Ensure that , Connect should be all way right before switching on the trainer. Switch off the S1 and S2 (to Take the reading without capacitor filter. Switch on the power. Note down the reading in the voltmeter and ammeter. These reading are DC rectified values. See the ripple output on to the CRO to observe the waveform and ripple amplitude. Repeat the reading with capacitor and pi filter by switching on the Switch S1, S2. See the difference of

filtered output and without filtered output. Record the reading in the table. Find the practical values